1. Field of the Invention
The present invention relates to a coating device for applying a coating material such as a magnetic solution, a sensitizing solution and a paint to a wide substrate of resin, paper, cloth, metal or the like.
2. Description of the Prior Art
In general, various coating devices are used to continuously apply various coatings to a continuous substrate of resin film, paper, cloth, metal or the like.
Such coating devices for applying a coating to such a substrate, which have been used, include a variety of coating devices such as a roll type coating device, a gravure coating device, an extrusion type coating device and the like. The present invention is directed to a coating device designed to discharge a coating under a proper pressure from a slit in a coating head, as is the extrusion type coating device or the like.
A coating device of such a type has a coating head suitable for a substrate having a width, for example, on the order of 0.5 to 3.0 m, so that a desired coating is discharged under a proper pressure from the slit in the coating head and applied to the substrate in such a manner that the coating head is pushed against the travelling substrate.
In such a coating device, the following problem is encountered, because the coating is discharged under the proper pressure from the slit defined in the coating head. Also because of the viscosity of the coating, the opening width of the slit at a longitudinal central point may be increased to a value larger than those at opposite ends and as a result, the widthwise thickness of the coating applied to the substrate is not uniform, thereby bringing about a reduction in coating accuracy such as an irregularity of thickness of the coating.
In order to overcome such problem, a coating device has been proposed in which the coating accuracy is enhanced by adjusting the opening width of the slit, as disclosed in Japanese Patent Application Laid-open No. 56272/90.
In the prior art coating device disclosed in Japanese Patent Application Laid-open No. 56272/90, however, a reservoir 3 is provided within the coating device 1 and connected to a coating supply port 2. The reservoir 3 has a widthwise dimension L corresponding to the width of a substrate 4 (FIG. 2). A slit 5 is defined by a back block 6 and a doctor block 7 for discharging a coating over the widthwise dimension. A yoke 8 and a screw 9a as a biasing/adjusting member attached to the yoke 8 are mounted on an outer peripheral wall of a side surface of the doctor block 7. The yoke 8 is mounted on an outer wall surface of the coating device 1, as shown in FIG. 10, and fixed by a screw 11a at an acting portion 11 closer to a tip end 10, and an adjusting portion 9 is provided at a yoke end remotest from the tip end 10 for applying a force to the acting portion 11. The screw 9a is disposed in the adjusting portion 9, so that the magnitude of the opening width t of the slit 5 can be adjusted by adjusting the screw 9a. The, yoke 8 is fastened at its vertically substantially central portion by a screw 12a to come into contact with to the side wall, but unlike the acting portion 11, the screw 12a need not necessarily firmly fix the central portion, and has a positioning effect, so that the central portion serves as a fulcrum 12 for the action of a lever.
Therefore, the operatability of adjusting the magnitude of the opening width t of the slit 5 for discharging the coating can be enhanced, but it is still necessary to adjust the longitudinal (in the widthwise direction of the substrate) magnitude of the opening width t of the slit 5, resulting not only in reductions in operatability and maintenance property, but also in a problem that a limitation in design of the structure of the coating device 1 is imposed and a problem of an increased economic burden.
A hot melt system comprising the heating of a coating to apply the coating suffers from a problem that the back block 6 and the doctor block 7 may be heated, so that they are liable to be deformed, and the clearance t is liable to be varied.
Accordingly, it is an object of the present invention to provide a coating device wherein the problems associated with the prior art can be overcome, and a coating can be applied widthwise uniformly on a substrate.
To achieve, the above object, according to the present invention, there is provided a coating device for applying a coating to a surface of a travelling continuous substrate by discharging it from a nozzle extending in a widthwise direction of the substrate, comprising a plurality of discharge openings arranged in a row at predetermined distances spaced apart from one another in a longitudinal direction of the nozzle, and a flat surface formed on at least a portion, of a tip end of the nozzle opposed to the substrate, which lies at a downstream side in a travelling direction of the substrate, the flat surface being adapted to permit the uniformization of the thickness of the coating discharged from the plurality of discharge openings onto the substrate.
In the coating device according to the present invention, the discharge openings may be arranged in multiple rows, so that a plurality of coatings can be applied in a superposed manner onto a surface of a travelling continuous substrate.
With the coating device having the above construction according to the present invention, the coating can be discharged onto the substrate from the plurality of discharge openings arranged in a row at the predetermined distances spaced apart from one another in the longitudinal direction of the nozzle, and the coatings discharged onto the substrate can be applied widthwise uniformly to the substrate with the aid of the flat surface. In other words, because the coating is discharged from the plurality of discharge openings having a longitudinally short dimension of length, it is possible to prevent the deformation of the discharge openings, and it is not necessary to limit the coating width to a small level, thereby enabling a wide coating. In addition, it is possible to provide a high quality coating having a uniform thickness.